_resolve_source now prefers the album's pinned canonical (source, album_id) when
set, before the source-priority walk. So once an album's canonical is resolved,
reorganize agrees with Track Number Repair (Stage 4) and stops mislabelling a
standard album as deluxe (#767-Bug2).
Gated + side-effect-free: only changes behavior for albums that already carry a
canonical (none do until the populate step runs), an explicit user source pick
(strict_source) still wins over the canonical, and a failed canonical fetch
falls through to today's priority walk. So this stage is behavior-neutral until
canonical is populated.
Tests: tests/test_reorganize_canonical_source.py (4) — canonical preferred over
priority, fetch-failure falls back, strict_source ignores canonical, no-canonical
unchanged. 113 reorganize-orchestrator/tag-source/unknown-artist tests still pass
(no regression).
